The adoptive transfer of human T lymphocytes that are engineered by gene transfer to express chimeric antigen receptors (CARs) specific for surface molecules expressed on tumor cells has the potential to effectively treat cancer. Chimeric receptors are synthetic receptors that include an extracellular ligand binding domain, most commonly a single chain variable fragment of a monoclonal antibody (scFv) linked to intracellular signaling components, most commonly CD3 alone or combined with one or more costimulatory domains. Much of the research in the design of chimeric receptors has focused on defining scFvs and other ligand binding elements that target malignant cells without causing serious toxicity to essential normal tissues, and on defining the optimal composition of intracellular signaling modules to activate T cell effector functions.
Although, T cell (CAR-T) adoptive therapy clinical trials (chimeric antigen receptor expressing T cells) are demonstrating potent anti-tumor activity, it is apparent that significant toxicities can arise, for example, engraftment-induced cytokine storm, tumor lysis syndromes and ongoing B cell cytopenias, each of which are attributable to unregulated functional outputs of constitutively expressed CARs. Such toxicities can in some context threaten to limit the applicability of CAR-T cell adoptive therapy. Clinical trials using transgene-modified adoptive T cell immunotherapies have only tested T cells that constitutively express the transgene, or are always in the “ON” state, contributing in large part to transgene associated side-effects. Suicide gene-mediated elimination of CAR-T cells can ameliorate such toxicities; however, this approach risks premature attenuation of anti-tumor activity and significantly impacts curative potential.
Current small molecule-regulated transgene expression technologies rely on a variety of drug inputs including macrolides, ecdysones and rapamycin analogs. Clinical applicability of these systems is limited due to toxic off target effects, unfavorable biodistribution and pharmacodynamics profiles, limited output dynamic range, and/or limited availability as FDA-approved commercially available pharmaceuticals. Furthermore, many of these systems use chimeric transcriptional regulators built from xenogeneic components, thus introducing the complication of immunogenicity when applying these systems to human therapeutics.
There is a need to identify methods for determining elements of chimeric receptor design that are important for therapeutic activity and cell populations to genetically modify and adoptively transfer that will provide enhanced survival and efficacy in vivo while minimizing adverse side effects. There is also a need for expression systems and methods for modulating cells for use in cell therapy, such as for modulating expression of recombinant antigen receptors such as CARs and/or other molecules expressed by such cells, such as to improve therapeutic activity, enhanced survival and/or efficacy in vivo and/or minimize adverse side effects.